This invention pertains to the art of construction of sheet metal gas burners and, in particular, to that part relating to the gas burner upstream end configuration for purposes of primary air inlet and air shuttering.
As noted in the cross-referenced related application, the heating capacity of different size gas-fired furnaces using heat exchanger assemblies of modular construction is common practice, with each module including a burner assembly. Since the amount of gas needed is a function of the number of heat exchanger modules used, the size of the manifold pipe bringing the gas to the burners varies accordingly. It is not uncommon to have the upstream end of the burners physically conform to the manifold pipe in its attachment. An example of this is shown in U.S. Pat. No. 3,567,137 in which the semi-circular end of the gas burner fits on a diameter of the manifold pipe. Since the heat exchanger modules are identical and any given adequate burner design can be the same for each of these modules, it is desirable to standardize the upstream end of the burner rather than vary its size to conform to the particular size of the manifold pipe.
Another problem with certain manifold mounting designs for gas burners comes from the different types of furnaces in which the burners are used. For example, counterflow furnaces and outdoor-type furnaces typically have their gas inlet manifolds located near the floor mounting surface of the furnace. Since with some arrangements the burners must be removed by passing them underneath the manifold pipe, the burners strike the floor that the furnace is positioned on. Also, sometimes burner removal over the top of the manifolds is not feasible because of physical interference with the heat exchangers secondary air inlet. Thus, in some cases the entire manifold must be dismantled and disconnected from the gas supply line before the burners can be removed.
Another aspect of the design of the upstream mounting and air inlet end of a gas burner relates to the provision of sufficient primary air in order to achieve complete combustion. The amount of primary air entering a burner is a function of the primary air inlet design, the size of the upstream end, the type of gas used, the spud gas jet design and obstructions in the airflow path. Thus, even if the upstream end design promotes servicing and easy removal, consideration must also be given to the provision of an efficient primary air inlet arrangement and one which avoids turbulent flow. Although the arrangements taught in U.S. Pat. Nos. 3,312,267 and 3,270,967 appear to be advantageous with respect to mounting the upstream ends of their particular burner designs on gas spuds, as distinct from upon the manifold itself, each of these patents include inlet air shutter arrangements which may be likened to sharp-edged orifices and are considered disadvantageous in that respect. It is one aim of our invention to provide an arrangement in which the advantages of mounting upon a spud are obtained, but without the disadvantages resulting from the sharp-edged orifice arrangement.
In another burner design, specifically that disclosed in U.S. Pat. No. 3,285,317, the upstream end of the burner is funnel-shaped and thus advantageous with respect to efficient flow. However, since the particular gas spud nozzle designs differ in accordance with the type of gas used and the gas pressure is also different with different gases, the regions within which the injected gas and primary air mix will be different in relation to the spud exit with different gases. In the funnel-shaped inlet in the noted patent, control of the gas and air mixing process is limited because of the fixed location of the funnel. It is another aim of our arrangement to avoid this limitation.
Another aspect of the inlet end configuration arises in the connection with the burning of high-density propane gas. Burning of this gas often results in sonic resonance and an intolerable level of noise. If proper control of the gas and air proportions in the mixing location is possible, this noise can be tuned out by adjustment. Since by design the manifold pipe is located in the path of the airstream parallel to the burner's center line, air flow into the burner interior is obstructed to a degree by the manifold. Some relief to this obstruction is available with designs such as taught in U.S. Pat. Nos. 3,312,267 and 3,270,967 which provide air entrances at the bottom half of the burner inlet. These arrangements also include the sharp-edged orifice problems as noted before. Further, the designs are also believed to require an increased burner size which is disadvantageous with respect to material requirements. Another aim of our invention is to avoid the disadvantages inherent in such arrangements.
Axially adjustable air shutters for controlling the admission of primary air are shown in each of U.S. Pat. Nos. 4,118,175; 3,312,267 and 3,270,967. However, in each of these the disadvantages of the sharp-edged orifice problem are at least among those problems arising from their particular configurations.
In summary, it is our aim to provide a burner inlet end configuration and mounting arrangement, along with an air shutter construction, which is considered advantageous compared to the various designs noted heretofore, and is relatively inexpensive in cost of materials and fabrication and has satisfactory operating characteristics.